1. Field of the Invention
This invention relates to a projector type head light of an automobile and, more particularly, it relates to an improvement to a head light comprising a converging reflector and a shade for defining the light distribution pattern within the head light as well as an aspherical projection lens for projecting light with the pattern along the axis of irradiation.
2. Background Art
FIG. 10 of the accompanying drawings schematically illustrates the arrangement of a conventional projector type head light. The projector type head light 90 comprises a light source 91 which is a halogen lamp, an elliptic reflector 92 having its first focal point located substantially on the light source 91, a shade 93 arranged near the second focal point of said elliptic reflector 92 and an aspherical projection lens 94 having its focal point located close to the second focal point of said elliptic reflector 92.
The elliptic reflector 92 is divided into a central section 92a, left and right lateral peripheral sections 92b, 92b and upper and lower peripheral sections 92c, 92c as shown in FIG. 11 in order to make it meet the requirement of having a wide horizontal angle of projection, said central section 92a having its second focal point f92a located near the focal point f94 of the projection lens 94 and on the optical axis of the optical system of the head light in order to irradiate the orthogonal front of the projector type head light 90.
Meanwhile, the lateral peripheral sections 92b, 92b have their second focal points f92b, f92b located at respective lateral positions that are significantly offset toward left and right on a horizontal plane from the focal point f94 of the projection lens 94 so that rays of light may be irradiated with a wide angle of projection. Of rays of light entering the projection lens 94 from said elliptic reflector 92, those that are not necessary for producing an intended light distribution pattern are blocked by the shade 93 and hence removed from the optical system.
By examining the relationship between the nature of rays of light reflected by the different sections of said elliptic reflector 92 and the light distribution pattern of the projector type head light, it will be found that, since an axially long filament called C-filament is normally used for the light source 91 of the projector type head light 90 of the type under consideration, an image of the filament is projected vertically by rays of light reflected from the central section 92a and the lateral peripheral sections 92c, 92c of the elliptic reflector 92 to show a vertically long but laterally narrow image, whereas the image of the filament projected horizontally by rays of light reflected from the lateral peripheral sections 92b, 92b tends to be vertically short and laterally wide.
Thus, rays of light from the relatively high central section 92a and upper and lower peripheral sections 92c, 92c of the elliptic reflector 92 are arranged in left and right lateral areas of the light distribution pattern close that are to the center, whereas those from the relatively low left and right lateral peripheral sections 92b, 92b of the elliptic reflector 92 are spread to the left and right so that the light distribution pattern HO becomes lowly profiled and substantially T-shaped as shown in FIG. 13 when upward beams are removed by the shade 93.
Such a T-shaped light distribution pattern HO of a conventional projector type head light 90 has a number of disadvantages. Firstly, the road lying ahead of the running automobile is particularly brightly lighted in an area immediately in front of it to reduce the visual sensitivity of the driver and therefore the lighting effect of the head light so that an auxiliary shade will have to be provided on the head light in order to lessen the brightness of that area, making the configuration of the head light rather complicated and reducing the overall quantity of light available for lighting.
Secondly, rays of light of the low profile light distribution pattern are further dispersed laterally to shed light sideways so that the curbs and the sidewalks are lighted only with such a low profile light distribution pattern to make the traffic signs hardly visible to the driver if they are arranged at high positions. These and other problems of conventional projector type head lights are to be dissolved to ensure reliable lighting on the part of automobiles.
From the above description, it may appear that the above problems are solved by confining rays of light coming from the lower lateral peripheral sections 92b, 92b to a central area of the light distribution pattern and laterally spreading the rays of light coming from the relatively high central section 92 and the lower lateral peripheral sections 92c, 92c. However, the size of the area of orthogonal projection C that allows projection of light orthogonally in front of the light distribution pattern 92 is limited for the reasons that will be described hereinafter by referring to FIG. 2(A) and rays of light coming from the left and right lateral sections 92b, 92b are excluded from this area of orthogonal projection C to make such an attempt not feasible.